Managing southern rust
Southern rust seems like a problem that wouldn’t affect farmers in the Northeast; however, Camilo Parada-Rojas, field crop pathologist with Cornell University, presented the on the topic at the annual CCE-sponsored Corn Congress because the pathogen is carried by wind currents and can spread this way.
“Rust spores are carried on wind currents from tropical areas into corn-producing areas,” Parada-Rojas said.
Southern rust spores land on leaves, infecting the new plant host. They produce more spores that spread to nearby plants. Once the infection begins, it spreads throughout the stand. When environmental conditions are right, secondary infections on plants in other regions begins.
Parada-Rojas specified that southern rust differs from common rust in a few ways. Southern rust is on only the upper leaf surface where common rust is on both upper and lower leaf surfaces. Southern rust is light orange and circular, whereas common rust is brick red in color and elongated in shape. The distribution is also different because southern rust is densely clustered and common rust is scattered on leaves.
Parada-Rojas suggested that mitigating several factors for managing southern rust can help reduce its spread. These include weather and movement, crop decisions and fungicide timing.
In June and July, heat waves combined with windy weather can move spores rapidly. Between 80º and 90º F, it’s “the perfect temperature for this pathogen,” Parada-Rojas said.
In June 2025, conditions were ideal for southern rust to spread with high wind speed and warm temps, but “luckily, that wind did not go northeast,” Parada-Rojas said.
He encouraged farmers to pay attention to the NOAA weather maps to remain aware of weather patterns that can spread southern rust.
“You have to rely on the network of land grant universities to identify where this pathogen is,” Parada-Rojas said. “Some seed companies say they have resistance to southern rust.”
He hopes that by 2030, genome edited seeds will offer resistance to southern rust.
“Scouting is very important, but also you have to think about what to do if it’s here,” he added. He encouraged scouting and harvesting the weakest fields first, even if the grain moisture is high.
Southern rust weakens the stalk strength. “Rust shuts down leaves,” Parada-Rojas explained. “The plant pulls energy from the stalk. Lodging risk rises.”
In addition, grain quality drops, as early plant death shortens grain fill. “Expect lighter test weight and smaller kernels,” Parada-Rojas said.
Southern rust does not survive in residue or soil. Tillage does not reduce risk for the next season.
“You have to rely on several tools to control pathogens so it won’t affect your yield,” Parada-Rojas said.
In U.S. field trials by Plant Health Progress in 2025, timely application of fungicide to shield the upper canopy included more than a dozen brands. The only one rated “excellent” was Trivapro® 2021SE at 13.7 oz./acre, which is the label rate. The rest ranked either good or good to very good (except for Tilt® 3.6 EC at 4 oz./acre, rated for 2.0 to 4.0.
“We may need to use drones to apply,” he said. “Some of these are not allowed for aerial applications or near bodies of water. The label is the law.”
He sees potential benefits of fungicide applications. Between VT and R2, the first spray is justified and a second spray is likely. By R3, a first spray is justified and a second spray unlikely. By R4 and later, do not spray, as “it’s too late and you won’t see an economic benefit,” Parada-Rojas said.
He is beginning research specific to New York. It’s not a sure bet the Empire State will see southern rust this summer.
“Potential for southern rust appearance in New York is hit or miss,” Parada-Rojas said. “Depending on spore transport and weather, it may not show up or it may arrive late. Check with your seed representatives. Southern rust resistance traits may be an insurance policy. Private breeding efforts are ongoing to provide robust disease resistance options.
“Fungicides are key in the management toolbox. It can protect susceptible hybrids or provide an extra layer of defense if applied timely.”
He wants any farmers who spot what they think is southern rust to report their suspicion to their local Extension office.
“Collaborative disease surveillance will be key to help you make decisions,” he added. “We want to send out a warning to other producers.”
